1. Field of the Invention
This invention relates to a spinal implant that holds and stabilizes the vertebrae of a vertebral column.
2. Description of the Related Art
When the vertebrae of a backbone are fused together it is critical that the vertebrae are in proper orientation with respect to each other and remain that way throughout the fusing process. One present method of insuring alignment is to attach a plate to the vertebrae, which holds the skeletal members in position during the fusing process. The plate is attached to each vertebrae by screws that are screwed into the pedicle of each vertebra. The plate has holes or slots that fit over the screws, wherein two nuts are located on each side of the plate to fasten the same to the screws.
Because the spine is curved, the plate must have a radius to conform to the shape of the vertebral column. To create such a curvature, the plate is usually bent by the surgeon in the operating room before the installation of the implant. The formation of the plate and the assembly of the implant is inexact, such that the plate and screws are typically at an angle to each other. This lack of perpendicularity causes the nuts to engage the member in an uneven manner, wherein it has been found that the nuts would break at the threads of the screws after installation.
Another type of spinal implant includes screws that have a lug at one end. The screws are screwed into the pedicles and a preformed rod is inserted through the lugs to connect the vertebrae together. The hole diameter of the lug is larger than the diameter of the rods, so that absolute perpendicularity between the two members is not required. The rod is secured to the screws by set screws which are inserted through the lugs and engage the rod. Set screws are not the most rigid means of attachment, wherein there is a possibility that the rod will disengage from the screws and allow the vertebrae to move relative to each other. Therefore it would be desirable to have an easy to install rigid spinal implant, that would not require perpendicularity between the screws and the tie rod.